The Black Elephant is Portland's first dedicated hostel, and it's an exceptionally good one, with funky interior art, exterior murals, a central location and a range of clean and comfortable rooms. The lobby and kitchen spaces are super-colorful and inviting, and there's even a 'vampire' themed bathroom.
The owners are really dedicated to the idea of a hostel as a shared, social experience, as opposed to just a cheap place to bed down. No one is going to force you to be friendly, of course, but there's a nice sense of community-mindedness here that's very appealing.
